The present invention relates to a control arrangement for an elevator brake, and to an elevator brake.
According to present standards, elevators are required to have a redundant braking system. For example, European Standard EN 81 relating to installation of machineroom-less elevators requires that all the mechanical components of the brake which take part in the application of the braking action on the drum or disk shall be installed in two sets. Each of the braking sets is required to be capable of providing a sufficient braking effort to slow down the car, e.g. traveling downwards at rated speed and with rated load, in case the other one the braking sets does not work.
Therefore, the functionality of the brake sets should be tested not only in cooperative operation of both brake sets, but also for each brake set alone. Such so-called single braking member testing requires to keep, temporarily for the course of the test, the braking member of one of the brake sets permanently released, while controlling the braking member of the other brake set according to normal operation.
Presently, retaining one of the braking members permanently in released state is done mechanically. A mechanical means is attached to the braking member to be retained in released state. This is comparatively easy for an elevator having a machineroom, where there is good access to the brake. However, in machineroomless elevators the machine unit is installed in the elevator shaft, typically at the top or bottom of the elevator shaft, and hence access to the elevator brake to apply such mechanical means for releasing the braking member is often difficult, e. g. requiring a service person to climb on the roof of the car and bring the car in a position where the elevator brake can be accessed. Due to these circumstances, the single braking member test becomes cumbersome.
There were made proposals to provide some kind of mechanical linkage (e. g. Bowden-cables) between the machine unit with the brake sets and an accessible position for manual activation of a permanently releasing of a braking member. These proposal aimed being able to move the elevator car to a safe position in case of an emergency, e. g. when the elevator car got stuck in the elevator shaft, see e. g. U.S. Pat. No. 6,021,872, U.S. Pat. No. 6,520,299, U.S. Pat. No. 6,817,453. However, such mechanical linkages have a number of disadvantages, particularly because there are constrains on the placing of the mechanical linkage, e. g. maximum distance and/or bending radii to be respected because of friction and/or limited wear resistance of mechanical linkages like Bowden cables.
U.S. Pat. No. 5,199,532 provides a proposal to provide an auxiliary coil for being able to release the braking member of an elevator brake, in case the primary releasing means such as a coil does not release when desired.
Therefore it would be beneficial to a have more convenient possibility for bringing the elevator system into a configuration for carrying out a single braking member test, particularly to be able to permanently release the braking member of one of the brake sets of the elevator brake without the need to have direct access to the elevator brake.